1. Field of Invention The present invention relates to a self-contained cartridge for launching a relatively low mass projectile at a low speed. More particularly, the invention relates to an apparatus for a gas charged cartridge and initiating mechanism for launching a lightweight projectile at a low velocity.
2. Description of the Prior Art There are several alternative prior art systems to achieve a low velocity launch of a light-weight projectile. One such system is to use a combustible propellant, such as gunpowder, which generates high-pressure gases upon initiation. These gases-then impinge upon the rear of the projectile to force it down the barrel of a gun weapon. Several types of powders can be utilized in such an application. The modern "smokeless" propellants burn progressively, that is, their burning rate increases as the chamber pressure increases. However, since the chamber pressures encountered when launching a light-weight projectile at a low velocity are far below those required by "smokeless" propellants to burn optimally, the result is a lack of shot-to-shot repeatability. Differing amounts of unburnt propellants are left after the firing event which cause large variations in muzzle velocity and peak pressure. An alternative propellant is "black powder", a substance that burns more consistently at lower pressures- However, black powder is an impact sensitive explosive, and can therefore be very dangerous to handle. Also, black powder produces highly corrosive salts and heavy residue among its combustion products, both of which are detrimental to the life of the weapon.
Compressed gas is also employed to propel projectiles of low sectional density. These systems utilize an initially pressurized vessel, or gas bottle, which is charged with a gas such as CO.sub.2. This bottle is used to charge a reservoir internal to the weapon, and then a valve is opened to allow the gas to impinge upon the rear of the projectile. However, these systems are both cumbersome to carry and time-consuming to load. Also, their performance is significantly degraded due to energy losses encountered through the valve, referred to as "valve losses." Furthermore, velocity variations are induced depending on the amount of time between reservoir charging and projectile firing. These are a result of the initial temperature drop undergone by the gas while the reservoir is charged and subsequent heating afterwards, which continuously changes the reservoir pressure. In addition, chamber pressures vary due to the pressure left in the bottle, especially if used for multiple shots.
Another system of projectile propulsion utilizes compressed ambient air. There are two basic means of operation; namely, pump or spring-air. The pump type uses a piston with a one-way valve which allows an internal reservoir to be charged. The pressure depends on how many times the manually operated lever is actuated. This system is subject to the same type of valve losses as mentioned above. Also, since the air is heated during the compression process, the reservoir pressure changes as the air cools. The spring-air type employs a compression spring which pushes a piston inside of a cylinder. The spring is compressed manually and is released with trigger pull. It then forces the piston to compress ambient air which is communicated directly to the rear of the projectile. This system provides better shot-to-shot repeatability than the previous systems. However, this type can only be used in a single shot mode, requiring the spring to be manually recompressed for each shot. Also, as the caliber of the weapon and the mass of the projectile increases, so must the spring force needed to achieve similar performance. Therefore, the spring quickly becomes too stiff for an operator to compress, even utilizing leverage.
3. Advantages over the Prior Art
The present invention relates to an apparatus for a gas charged cartridge and initiating mechanism for launching a projectile of a relatively low mass at a low velocity (less than 300 m/s). Apparatus of this type is useful for propelling a non-lethal projectile such as a hypodermic dart or throwing of a line from ship to ship. The cartridge itself is a reservoir which is charged with compressed air. The reservoir is sealed on the end facing the projectile with a burst diaphragm (or a rupture-type disk). The apparatus also incorporates a means of rupturing the diaphragm. The rupturing is accomplished by either a rupture rod attached to rear of the projectile or by an electric squib associated with the diaphragm. During firing, the diaphragm is punctured, quickly releasing compressed gas to propel the projectile forward down the barrel of a gun weapon.
The apparatus of the present invention has a number of advantages over the prior art. First, the apparatus provides a means of launching a relatively low mass projectile at a highly consistent velocity. Second, the apparatus performs its operation in a highly efficient manner since its use of a diaphragm virtually eliminates both valve and pipe losses. Third, the apparatus uses a relatively small, one-piece package which requires no accessory or ancillary equipment, such as a gas bottle. Fourth, the apparatus allows for long term storage under harsh ambient conditions, while not requiring any special maintenance or care to retain its original performance. Fifth, the apparatus lends itself for use as a single-shot weapon, a semi-automatic weapon, or a fully-automatic weapon. Lastly, the cartridge and launcher apparatus is of low cost due to its simplicity and low operating pressures.